P0128 KIA Coolant Thermostat Malfunction

Possible causes
– Leaking or stuck open thermostat
– Low engine coolant level
– Insufficient warm up time
– Faulty engine coolant temperature sensor
– Engine coolant temperature sensor harness is open or shorted
– Engine coolant temperature sensor circuit poor electrical connection
Tech notes
If cooling system is not leaking and the fluid level is OK, replacing the thermostat usually takes care of the problem.
When is the code detected?
The engine coolant temperature does not reach to specified temperature even though the engine has run long enough.
Symptoms
– Engine Light ON (or Service Engine Soon Warning Light)
P0128 KIA Description
Indicates that the thermostat monitor has not achieved the required engine operating temperature within a specified amount of time after starting the engine.
KIA Technical Service Bulletins for P0128 code
2010 KIA SOUL ENGINE AND ENGINE COOLING:ENGINE
2006 KIA RIO ENGINE AND ENGINE COOLING:ENGINE
2007 KIA RIO ENGINE AND ENGINE COOLING:ENGINE
2008 KIA RIO ENGINE AND ENGINE COOLING:ENGINE
2008 KIA RIO ENGINE AND ENGINE COOLING:ENGINE
2009 KIA RIO ENGINE AND ENGINE COOLING:ENGINE
2009 KIA RIO ENGINE AND ENGINE COOLING:ENGINE
2001 KIA OPTIMA ELECTRICAL SYSTEM:IGNITION:MODULE